As a power unit mounted on a vehicle, a suspension arrangement structure equipped with a belt-type infinitely variable transmission and a differential gear is well known. For example, Japanese Utility Model Publication Laid-open No. 62-54891 is related art and is described with reference to FIG. 23 below. FIG. 23 is a side view showing the structure of a power unit of the related art, where a power unit 300 mounted on a scooter type three-wheeled vehicle comprises an engine 301 and a transmission unit 303 linked to a crankshaft 302 of the engine 301, and has a wrapping transmission 304 housed in the transmission case of the transmission unit 303. Left and right driving wheels 311 are linked to the rear lower section of the wind-type transmission 304, via a gear reduction mechanism 306, a differential gear 307, and an axle arm 308.
The above mentioned axle arm 308 is directly fitted from the differential gear 307 to the driving wheels 311, so that the left and right driving wheels move up and down integrally. For example, when one of the driving wheels 311 runs over a bump on the surface of a road, the driving wheel 311 moves upwards. The axle arm 308 therefore tilts and the vehicle body rolls. Such a structure does not have a problem when being adopted in a vehicle with small displacement. However, since ride quality is affected when being adopted in a vehicle with middle or more displacement capable of high speed operation, the structure required improvement.
With the above mentioned three-wheeled vehicle, it is also required to have a structure capable of swinging the vehicle body left and right in order to obtain the same driving performance as that of two-wheel vehicle. For example, the left and right driving wheels 311 are supported by an independent suspension arm to be independent suspension. Also, even when a vehicle body equipped with a power unit is swung to the left and right, if it is possible to prevent the suspension arm from interfering with the power unit, a swinging three-wheeled vehicle with improved comfortable ride can be achieved.
The object of the present invention is to easily construct an independently swinging suspension type three-wheeled vehicle by improving a suspension arrangement structure for a vehicle.